Abstract
Introduction
Patellar mobilisation methods used during total knee arthroplasty (TKA) have been debated in the literature, with some proponents of minimally invasive TKA suggesting that laterally retracting, rather than everting the patella may be beneficial. It was our hypothesis that by using randomised, prospective, blinded study methods, there would be no significant difference in clinical outcome measures based solely on eversion of the patella during total knee arthroplasty.
Methods
After an a priori power analysis was done, 120 primary total knee replacements indicated for degenerative joint disease were included in the study and randomised to one of two patella exposure techniques: lateral retraction or eversion. Short-term outcomes were evaluated during hospitalisation and included time to return of straight leg raise (SLR), ambulation distance, and length of hospital stay. Long-term outcome values were evaluated pre-operatively, at 6 weeks, 3 months, and 1 year post-operatively, and included leg extension strength measured by dynamometer, knee range of motion (ROM), Visual Analog Scale (VAS) pain before and after knee motion, circumferential thigh measurements, and SF-36 Physical and Mental Component Scores (PCS, MCS). All collaborating investigators were blinded to each other's data. Surgical techniques and perioperative arthroplasty management protocols were those routinely and currently used during total knee replacement surgery at our institution.
Results
1 year follow-up data was available for 88.3% of patients. Mixed model analysis of variance showed no statistically significant differences between the two groups with respect to short or long term outcome measures. Ambulation distance improved dramatically from 24 (28±46 ft) to 48 hours (71±64; p<0.001) but was not different between groups (p=0.79). 24 of 51 retraction patients could straight leg raise within the first 24 hours versus 24 of 46 in the eversion group (p=0.69). At 48 hours, 23 of 48 and 31 of 53 respectively could SLR, (p=0.55). Improvements in VAS pain at rest were similar between groups (p=0.18–0.89), as were improvements in VAS pain after ROM (p=0.21–0.57). At 1 year postoperatively, quadriceps strength was not different between groups (p>0.5), and ROM improved by 6±18° from pre-operative values (p<0.001) with no statistically significant difference between groups. SF-36 PCS and MCS significantly improved for both study groups from preoperatively to 1 year postoperatively (time effect p<0.001) with similar effects between groups, and were not statistically significantly different at 1 yr after surgery (PCS: eversion 47.0±8.7, retraction 50.0±8.5, p=0.09), (MCS: eversion 53.7±9.0; retraction 53.0±10.3, p=0.69).
Conclusion
With proper surgical technique and attention to detail, we believe that the standard medial parapatellar approach with anterior tibial translation can provide an excellent surgical exposure without compromising the surrounding soft tissue envelope. At times, exposure can be augmented by eversion of the patella, and in our subjective experience, this has not led to inferior post-operative results compared to lateral retraction of the patella. Results of this study give objective support for these observations.
